There are two known strategies to diminish the noise transmitted through a glazing. First, an adequate dimensioning of the glass structure itself, which may be comprised of several layers, to which a noise and vibration absorbing material is integrated. A configuration adapted to the outlying joint assures the sealing between the glass and the rest of the structure.
The second approach consists of optimizing the joint's mechanical properties, for example its rigidity and/or its loss factor through absorption and its geometry.
All of these solutions quickly encounter physical limits and no longer satisfy current needs, particularly in the aviation sector. In addition, the dimensioning of a multi-layered glazing to include acoustic criteria proves to be particularly sensitive in the case of complex, thick and initially multi-layered windows like those in the cockpit of a plane. These windows must satisfy multidisciplinary constraints: resistance to bird impact, resistance to lightning, good optical transparency, reduced mass, etc. They are also subjected to a particularly high temperature gradient (−40° C. on the exterior of the plane, +20° C. on the interior).
Regarding the specific dimensioning of the joint for acoustic criteria, the applications affect thin windows, essentially for automobiles. A condition necessary for the acoustic efficiency of this device is that the assembly of the glass/joint duo to the rest of the structure allows the joint to work and dispel energy according to the mode of operation for which it was designed. Its rigidity and loss factor through absorption must be barely modified by the rest of the structure. And yet, the current assembly of cockpit windows does not satisfy this condition: they are inserted in the frame, they burn under the effect of pressurization in flight, the conditions to the limits are thus modified at the periphery. In addition, in the case of the cockpit, the temperature gradient (−40° C. on the exterior of the plane, +20° C. on the interior) imposes a choice of materials made up of the neutral joint in relation to the temperature, which strongly limits the usable materials.